Alkylation . Alkylation is commonly used to increase the performance of a certain product.
Summary
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- 1 Alkylation process
- 2 Aniline alkylation process
- 3 Catalysts used in alkylation
- 4 Alkylation Using Liquid Hydrogen Fluoride
- 5 Reverse reactions or dealkylation
- 6 Sources
Alkylation process
To increase the yield of a certain product, alkylation is commonly used and involves the conversion of, for example, an amine into its alkylated counterparts, as is the case of the reaction of aniline with methyl alcohol in the presence of a catalyst such as acid sulfuric. Aniline, with a considerable amount of excess methyl alcohol and a certain amount of sulfuric acid, is heated in an autoclave to around 200 ° C for 5 or 6 hours, to a high reaction pressure that can reach 540 lb / in2 ( 3.7 MPa). Then, vacuum distillation is used to carry out the purification of the final product.
Aniline alkylation process
In the aniline alkylation process to obtain di-ethylaniline by heating the aniline together with ethyl alcohol, sulfuric acid cannot be used since an ether will be formed; consequently, hydrochloric acid is used, although these reaction conditions are so corrosive that the steel used to resist pressure must have replaceable enamel coatings. Alkylation reactions using alkyl halides are carried out in an acidic medium. For example, hydrobromic acid is formed when methyl bromide is used in the alkylation reaction, and the use of an autoclave having an enamel coating and a lead-coated coating is suitable for such reactions. Alkylation in the oil refining industry == In the oil refining industry, alkylation is nothing more than the union of an olefin with an aromatic or paraffinic hydrocarbon. The alkylation processes are exothermic and are fundamentally similar to the polymerization processes of the refining industry, although they differ from these in that only part of the feed must be installed. As a result, the alkylated product does not contain olefins and has a higher octane number. These methods are based on the reactivity of the tertiary carbon of isobutane with olefins such as propylene, butylenes and amylenes.
The alkylated product is a mixture of saturated stable isoparaffins that distill in the gasoline range, making them the most desirable component of many high octane gasoline. The alkylation processes are exothermic and are fundamentally similar to the polymerization processes of the refining industry, although they differ from these in that only part of the feed must be installed. As a result, the alkylated product does not contain olefins and has a higher octane number. These methods are based on the reactivity of the tertiary carbon of isobutane with olefins such as propylene, butylenes and amylenes. The alkylated product is a mixture of saturated stable isoparaffins that distill in the gasoline range, making them the most desirable component of many high octane gasoline.
The alkylation processes are exothermic and are fundamentally similar to the polymerization processes of the refining industry, although they differ from these in that only part of the feed must be installed. As a result, the alkylated product does not contain olefins and has a higher octane number. These methods are based on the reactivity of the tertiary carbon of isobutane with olefins such as propylene, butylenes and amylenes.
Catalysts used in alkylation
The alkylation is carried out using any of these catalysts:
- Hydrogen fluoride
- Sulfuric acid
Alkylation Using Liquid Hydrogen Fluoride
During the alkylation process using liquid hydrogen fluoride, the acid can be used repeatedly, and there is virtually no problem with its final disposal. The acid / hydrocarbon ratio in the contactor should be 2: 1, and temperatures ranging from 15 – 35 ºC can be maintained in it, since refrigeration is not required. Anhydrous hydrofluoric acid is regenerated by distillation applying a pressure value sufficient to keep the reacting compounds in the liquid phase. In many cases, the use of steel is sufficient to build the alkylation equipment, even under the presence of strong acid catalysts, since its corrosive effect is greatly diminished due to the formation of esters as intermediate catalytic products. In the petroleum industry, the sulfuric acid and hydrogen fluoride that are used as catalysts for the alkylation process should be substantially anhydrous to be effective, and the use of equipment made of steel will suffice. When anhydrous conditions are not available, the use of equipment covered with lead, Monel or enamels is satisfactory. In a few cases, copper or tinned copper is still used, for example in the manufacture of pharmaceutical and photographic products, in order to reduce metal contamination. Usually the most convenient procedure to recover the product is distillation, even in those cases where the boiling point values of the various components are very close to each other. Frequently, distillation will supply a finished product of sufficient quality to meet market demands. If not, other purification methods may be employed, such as crystallization or solvent separation. The selection of the suitable solvent will lead, in many cases, to the crystallization of the alkylated products and consequently to their convenient recovery.
Reverse reactions or dealkylation
The reverse reactions, called dealkylation and hydro-dealkylation, are widely used to convert the available feeds into other desirable or highly demanded compounds. Two of these processes are:
- The conversion of toluene or xylene, or higher molecular weight alkyl aromatic compounds, to benzene, in the presence of hydrogen and of suitable amounts of a dealkylation catalyst, and
- The conversion of toluene to benzene plus xylenes mixed, in the presence of hydrogen and a fixed bed catalyst.
